1. Field of the Invention
The present invention relates to a sheet stack cutter for cutting sheet stacks set on a sheet loading table, and an improvement of a sheet stack cutter which performs a set-justification on the sheets formed with images by an image forming apparatus into sheet stacks and performs a cutting-justification with previously determined cutting-plane lines.
2. Description of the Prior Art
In general, this kind of sheet stack cutter has widely been served as the cutter which sets the paper sheets on the sheet loading table and performs cuttings at the determined portions. For example, this apparatus is known as a trimming apparatus or a cutting apparatus, the trimming apparatus performing the set-justification to the sheets delivered from a printer into the stacks for book-binding and performing a cutting-justification to the book-bound sheet stacks around perimeters, and the cutting apparatus performing the cutting on the sheets from the image forming apparatus into ½ or ¼.
There have conventionally been known a cutting apparatus which sets one sheet of paper on a table and cuts it as disclosed in, for example, a patent document 1 (Japanese Patent Laid Open No. 10-138194), and a cutting apparatus which sets many sheets of papers in stack and cuts at once as disclosed in a utility model document 2 (Japanese utility model publication No. 47-8308). With regard to the cutting ways, as the patent document 1, the cutting is carried out with a cutter edge (rotating cutter edge) from one end to the other end, and as the utility model document 2, the cutting is carried out with a flat cutter edge (guillotine) moving down from the upper part of the sheet stack.
As the patent document 1, in the mechanism of cutting by traveling one sheet of cutter edge (rotary knife) from one end of the sheet to the other end, if cutting the sheet stack of many paper sheets at once, a shearing force acting to the cutter edge becomes large, and if traveling the cutter edge with a force exceeding it, a problem is known as occurrence of the cutter edge meandering. Therefore, for cutting one sheet or a few sheets of papers, the cutting mechanism of rotating cutter edge has been conventionally employed. Accordingly, it has been assumed to be impossible to carrying out the cutting of many sheets of papers.
As the utility model document 2, when cutting many sheets of papers at once by means of a vertically moving cutter edge (guillotine), the shearing energy required to cutting must be large. This is because by bringing down the cutter edge at high speed, the sheet stack is cut at its impulsive force, and in this case, the apparatus must be stoutly composed and a driving apparatus must be large-scaled.
The utility model document 2 and a utility model document 3 (Japanese utility model publication No. 52-103489) have proposed the devices for reducing dimensions of the driving mechanism for vertically bringing the plate shaped cutter edge. The documents pivot the plate shaped cutter edge onto a pair of left and right swinging arms in order to swing the cutter edge. By causing the vertically moving cutter edge to swing by the pair of arm members, when the cutter edge reaches a lower dead point (finishing posture of cutting), shock loading to the apparatus can be reduced. Therefore, it is not necessary to stoutly compose the apparatus. Further, the utility model document proposes to make the pair of left and right swinging arms have different lengths so that the cutter edge tilts with respect to the sheet surface in order to reduce cutting force.
When loading to hold the plural sheets of papers on the sheet loading table and cutting them, the guillotine cutting system disclosed in the utility model document 2 is known. Similarly to such a cutting apparatus, the apparatus cutting the sheet stack from one end to the other end of the cutting plane line as swinging the plate shaped cutter edge is known from the utility model documents 2 and 3.
In each of the above cutting apparatuses, it is necessary to provide a cutter edge receiving member or the stationary cutter edge to the side of the sheet loading table with respect to the moving cutter edge vertically moving in the cutting direction. The cutter edge receiving member is composed of a soft material, for example, a rubber material not to damage the edge of the movable cutter, and the stationary cutter has the edge sliding with the edge of the movable cutter like scissors.
Conventionally, in the cutting mechanism holding the sheet stack between the moving cutter edge and the stationary cutter edge, if a space is created between both cutting edges, the cutting is impossible and the sheets enter therebetween to cause bad action (cutting jam). In case of cutting the sheet stack as creating the space between the cutting edges, a known problem occurs of inferior cutting quality.
Therefore, the prior art has employed a mechanism that the moving cutter edge is urged by such as a spring in the direction crossing with the cutting in order to suppress the stationary cutter edge. However, when cutting the sheet stack, large force acts in the direction crossing with the cutting, so that the moving cutter edge gets away from the stationary cutter edge and the space occurs between the cutting edges. Accordingly, when the prior art urges the moving cutter edge to suppress the side of the stationary cutter edge with the urging force overcoming the escaping force occurring when cutting the sheet stack, and troublesome works are involved as repairing or changing the cutting edges.
An inventor of this invention has hinted to position the stationary cutter edge to be placed to the side of the sheet loading table by suppressing it with an urging spring when closely sliding the moving cutter edge and the stationary cutter edge, and under this condition, to position the stationary cutter edge with the pressing means of forcing the sheet stack toward the sheet loading table.
It is a main object of the invention to provide a sheet stack cutter enabling to always realize exact cuttings of a superior cutting quality without effecting an overload on the cutting edges when cutting the sheet stack with the moving cutter edge and the stationary cutter edge along a predetermined cutting plane line.
Further, it is another object of the invention to the sheet stack cutter of a simple structure at lower cost when closely sliding the moving cutter edge and the stationary cutter edge each other.